Lets start with the type. I'm assuming its a silver arrowana? Asian Arowanas are illegal in many places and can grow to massive lengths. Arowana in general can get pretty huge. Arowana are not easy fish to care for they require huge tanks and constant care. They can get enormous plus they can jump like crazy. You will have to be prepared to put money into a firm lid. Since you say you don't know anything about them I would say do NOT buy it. Arrowana are not for the faint hearted or newbie, they are an advanced fish that should only be purchased if one knows exactly what they are doing.
This is an old post from June and this person is no longer a member.
I noticed it was an old post but it was such an interesting subject that I wanted to hear what everyone thought. Differently not the type of fish that most hobbyist should own.